1. Field of the Invention
This invention relates to an improved process for manufacturing artificial tanned hides possessing characteristics very similar to those of natural tanned hides.
Various processes, some of long standing, are known for manufacturing artificial leather. These processes may be divided into two large categories:
processes which use only synthetic materials, PA1 processes which also use natural products, such as scrap pieces of natural tanned hides or leather, the process according to the invention being more closely related to these processes.
The processes of the latter type have been subjected to much study and improvement, with the common object of achieving characteristics for the obtained product which approach the characteristics of natural hides.
2. Description of the Prior Art
The main method used in the past has been to finely triturate leather offcuts or tanned waste pieces from tanneries, and then mix this triturated material with natural or synthetic binders to form a semidense mix. This mix is then formed into a layer which, after pressing and drying, forms the required artificial leather.
In order to improve the mechanical characteristics of the products obtained by these processes, namely resistance to tear on the one hand and softness and other comfort-linked characteristics on the other hand, processes have been more recently proposed (see for example French Pat. No. 1,348,716 and U.S. Pat. Nos. 3,223,551, 3,285,775, 3,345,201) according to which a mass of finely ground leather fibres kept in non-colloidal aqueous suspension is applied to synthetic fibre supports, making the individual leather fibres separately penetrate into the support by mechanical and chemical means, and fixing the fibres on to the synthetic fibres of the support, preferably using binders based for example on dissolved nylon.
The process is very complex (both from the mechanical and from the chemical-physical viewpoint) and is complicated and strongly limited in its application by the need to use, as the initial material, leather fibres which have undergone a tanning process the parameters of which are strictly defined, and are then ground under pH conditions which are likewise strictly defined. In this respect, small variations either in pretanning or in the grinding conditions can make the leather fibres incapable of penetrating the synthetic fibre felt. This latter must in its turn be prepared under conditions which are also limiting (non-hydrophilic fibres, defined structure density etc.).
The problem of making the ground leather fibres penetrate the synthetic felt is evident, in all its difficulty, from German Pat. No. 1,930,523 or from French Pat. No. 2,040,211, which attempt to obviate the aforementioned limiting conditions by spreading the ground leather paste on to textile or non-woven fabric supports, and making the ground leather fibres mechanically penetrate and become bound to the synthetic fibres by needle action on the wetted material. However this system generates considerable equipment problems, as the operation has to be carried out under moist conditions on needling machines designed and constructed to operate under dry conditions, and special stainless steel sawtooth needles have to be used for this purpose, which amongst other things are relatively fragile.
A process has also been proposed, namely that described in French Pat. No. 2,105,639, in which leather or possibly natural collagenic substance is dissolved in more or less concentrated sulphuric acid, and the solution is mixed with other strongly acid solutions of nylon or another high polymer dissolved in concentrated hydrochloric acid. This polyamide-collagenic solution is then applied to a cotton support. However, this type of process has the disadvantage that the extremely acid solution degrades both the material forming the support and the leather fibres, so as to result in a material of modest physical characteristics. In this respect, the action of these acids is so violent that the protein fibres give a precipitate which, after drying, assumes a dry and fragile or corneous physical structure, of no real practical use.